<script src="jquery-1.10.1.min.js" type="text/javascript"></script>

<script type="text/javascript">
  $(document).ready(function(){
    $('.plus').on('click',function(){
      var clone = $('#abstract').clone();

      var html = clone.html();
      html = $('<div>'+html+'</div>')
      $("#container").append(html);

      ////////// REMOVE ADD + ///////////////
        var plusClone = $(this).clone();
        $(this).remove();
      ///////////////////////////////////////
    });
  });
</script>

<div id="container">
  <div id="abstract">
    <input type="text" class="txt" />
    <span class="minus zoom">(-)</span><span class="plus zoom">(+)</span>
  </div>
</div>

<style>
  input{
    font-size:25;
  }
  .zoom{
    font-size:30px;
    margin:10px;
    cursor:pointer;
  }
  .plus{
    color:green;
  }
  .minus{
    color:red;
  }
</style>




